JP4563001B2

JP4563001B2 - Flat rectangular battery

Info

Publication number: JP4563001B2
Application number: JP2003194961A
Authority: JP
Inventors: 正美鈴木; 幸司加納
Original assignee: Toshiba Battery Co Ltd
Current assignee: FDK Twicell Co Ltd
Priority date: 2003-07-10
Filing date: 2003-07-10
Publication date: 2010-10-13
Anticipated expiration: 2023-07-10
Also published as: JP2005032507A

Description

【０００１】
【発明の属する技術分野】
本発明は、扁平角形電池に係り、特に外装ケースに生じるスプリングバックと、内装ケースの変形を防止し、封口性を向上する扁平角形電池に関する。
【０００２】
【従来の技術】
携帯電話やＰＤＡなどの小型情報端末を中心に使用機器の小型化が加速しており、主電源である二次電池についても小型化を図ることが要求されている。これに対し、特許文献１、特許文献２に示すような負極端子を兼ねる金属製の負極ケースと、正極端子を兼ねる金属製の正極ケースが、絶縁ガスケットを介し嵌合され、さらに前記正極ケースまたは負極ケースが加締め加工により加締められた封口構造を有し、その内部に少なくとも正極、セパレータ、負極を含む発電要素と、非水電解質を内包した扁平形非水電解質二次電池において、扁平形電池の扁平面に垂直な方向の断面を見た場合に、少なくとも３面以上の正極と負極がセパレータを介し対向している正負極対向面を有した電極群が収納され、かつ、電極群内の正負極対向面積の総和が絶縁ガスケットの開口面積よりも大きい扁平形非水電解質二次電池が小型化の要求を満たす電池として提案されている。
【０００３】
【特許文献１】
特開２００１−０６８１６０号公報
【特許文献２】
特開２００１−０６８１４３号公報
【０００４】
さらに、最近になり液晶をはじめとした表示装置を有する小型機器は、薄型化を進める一方、表示装置の小型化には実使用上限度があるため、機器全体に占める表示装置の占有面積比率を極力大きくして、機器全体を小型化することが検討されている。この表示装置の多くは角形状を有していることから、この形状に機器を合わせるため機器全体が角形状を有するものが多くなっており、機器内での電池の搭載には周縁部に少なくとも２つ以上の直線部を有し、各直線部の端部が略円弧状曲線部により結ばれている角形や小判型に代表される小型の扁平形電池が望まれている。
【０００５】
しかしながら、従来のＬｉイオンやニッケル水素二次電池に見られるような深絞りをした外装ケースに封口板をレーザ溶接して封口している電池では、薄缶の製缶や電極挿入などの組立工程上の制約から電池の小型化に対してほぼ限界に来ている。
【０００６】
そこで、より小さく薄い略角形状を有する電池を製作するには新たな封口構造を用いた電池が必要であり、金属製の外装ケースと内装ケースが内部に電極を保持した状態で絶縁ガスケットを介し嵌合され、さらに外装ケースを加締め加工により封口部を形成した電池が望ましい。
【０００７】
しかしながら、周縁直線部をもつ扁平角型電池を従来のコイン形やボタン形の電池と同様に外装ケースの開口部を１／８〜１／４円弧に加締めた場合、外装ケースの周縁直線部にスプリングバックが生じ封口が甘くなったり、外装ケースを加締める際に内装ケースの側壁が内側に内傾や湾曲を起こし、十分な封口性を得ることはできなかった。特に電池が蒸気圧の高い高温高湿下に保存された場合、多大な影響を受け、外部から電池内に水分（水蒸気）が浸入し電池の開路電圧を大きく低下させたり、あるいはガス発生を招き電池を膨れさせたりした。前者は電池の電源としての基本機能を低下させ、後者は規格寸法外に電池が膨れ、薄型化された使用機器に変形や損傷を与えるので、その改善が望まれていた。
【０００８】
従来のコイン形やボタン形の電池の場合、内装ケースに内傾が生じようとすると、内装ケースの開口部の半径が小さくなるため、ケース基材には円周方向に均一な圧縮応力が働く。これに反発する梁の作用が内装ケースに働くため、円形の内装ケースにはケース側壁の内傾や湾曲（陥没）は生じ難かった。しかしながら、周縁直線部を有する電池において、周縁曲線部は従来の円形電池と同様に梁による作用が働くものの、周縁直線部は実質的に曲げ加工を行われた平板に近いものであり、梁の作用が働かず、外装ケースを加締め加工する際に働く圧縮応力に対し耐力が弱く、内装ケース側壁の内傾や湾曲が生じた。その結果、期待した封口性は得られず、また、内装ケースの湾曲を防止するために外装ケースの加締め加工圧力を弱めた場合、それに伴い、ガスケットの圧縮率の低下と外装ケースのスプリングバックの増加を招き、所望の封口性を得ることはできなかった。
【０００９】
【発明が解決しようとする課題】
本発明は上記情況に対処するためになされたもので、その課題は、外装ケースの加締め加工時の内装ケースの内傾及び湾曲と加締め後の外装ケースに生じるスプリングバックを防止し、かつ、封口部の強度を高め、電池が高温高湿下に置かれても開路電圧の低下が少なく、しかも、電池総高の増加の少ない扁平角形電池を提供することにある。
【００１０】
【課題を解決するための手段】
本発明者等は鋭意研究を重ねた結果、金属製の外装ケースと金属製の内装ケースが、電池の扁平面に対し鉛直方向に絶縁ガスケットを介し嵌合され、さらに前記絶縁ガスケットの外周側に配置された前記外装ケースが加締め加工により加締められた封口構造を有し、かつ電池の厚さが外寸よりも小さく、周縁部に少なくとも２つ以上の周縁直線部（以後、周縁直線部Ｂとする）を有し、前記直線部の各々の端部が周縁曲線部（以後、周縁曲線部Ａとする）により結ばれている扁平角形電池において、前記周縁曲線部の加締め形状が曲線であると共に、前記周縁直線部に該当する部位の前記外装ケースが、前記外装ケースの先端と加締め曲げ部との中間に直線部を設けた形状に加締められたことで、加締め加工時の内装ケースの内傾及び湾曲と外装ケースに生ずるスプリングバックを防止するとともに、封口強度を高め、電池が高温高湿下に置かれても外部からの水分の浸入を防止できることを見出した。
【００１１】
本発明者等は外装ケースの加締め挙動に注目し解析を行った結果、従来の円型電池と同様に外装ケースの先端を内側に向けて１／８〜１／４円弧を有する形状に加締める場合、周縁直線部において加締めが進行する過程で外装ケースの側壁がケースの底部周辺から一旦、過度に内傾した後、加締め金型のＲ形状に沿う形に加締められる挙動をとることを見出した。このため、加締めの中間過程で側壁底部から倒れ込んだ外装ケース側壁が内装ケース及び絶縁ガスケットを圧迫し、内装ケース側壁の内傾や湾曲を招いていることをつきとめた。
【００１２】
本発明者等は改善を図るために種々の対策を検討した結果、外装ケースの加締め形状を電池の肩Ｒ部全体に渡り１／８〜１／４円弧を設けた従来のアール形状から、外装ケースの先端と加締め曲げＲ部の間に直線部を設けた形状とし、加締め曲げＲを従来より小さな円弧として繋いだ形状に変更することで内装ケースに生じていた変形を防止できることを見出した。
【００１３】
また、外装ケースに直線部を設けた形状とすることでこの直線の末端である外装ケース側壁の中央付近に折り曲げ荷重が集中するため外装ケースを側壁中央付近から無理無く折り曲げるように加締めることができる。折り曲げの支点がケース側壁底部から側壁中央に移るためケース先端が内寄りに移動する移動量が減るとともに、外装ケース側壁がガスケット側部並びにその内側の内装ケースに加える押し圧を低減することができ、その結果、内装ケースの変形を防止することができる。
【００１４】
さらに、側壁中央を折り曲げることで封口部の硬性を向上させることができ、優れた封口性を長期に渡り維持することができる。この時、外装ケースに設けた直線部に繋がる加締め曲げ部の曲げ半径は、外Ｒで外装ケース基材板厚の４倍以下とするのが特に好ましく、曲げ半径を小さくすることで加締め曲げ部に曲げ荷重が集中し、外装ケースを側壁中央付近から折り曲げ易くなり、ケース底部からの側壁内傾を防止する効果をより高められる。さらに、曲げ半径の小さい方が折り曲げ部に生じる歪も大きくなるためその後のスプリングバックも生じ難い。
【００１５】
従来の円形電池では、外装ケース先端の曲げ半径を大きく取る方がガスケットの圧縮率を高められることから封口性は向上し、通常は板厚の５〜６倍の曲げ半径を採用して外装ケース先端を１／８〜１／４周の円弧状に加締めるが、この点で周縁直線部をもつ本発明の電池は従来の円型電池と大きく異なる。
【００１６】
ただし、本発明の電池において、加締め曲げ半径が基材厚さの１．５倍未満となる曲げ半径は小さすぎるため加締め曲げ部の金属ケース表面や金型表面に細かな傷が生じやすく、出来あがった電池の外観が劣ることがあり、曲げ半径を基材厚さの１．５倍以上とするのがさらに好ましい。
【００１７】
次に、本発明者等は、外装ケースに直線部を残し加締めることで封口部の強度が向上したことに注目し、加締め加工後の外装ケースに設けた直線部の折り曲げ角度について検討を重ねた。その結果、加締め後の直線部を、外装ケース側壁と概ね直交させ、外装ケースに設けた直線部を外装ケース底面に対し、水平角度で２５°〜−１５°の範囲に保つと水平方向の応力やケース基材の反りに対し、著しく強くなり、厳しい条件の外部環境に電池が置かれた場合でも封口部の変形が生じ難く、外部からの水分の浸入を長期に渡り抑制できることを見出した。また、水平角度が−１５°より小さいと、外装ケースの先端の直線部端が内装ケースの張出し部を過度に押し下げてしまい、内装ケースに変形をきたしたり、外装ケース中央の加締め曲げ部が外装ケース先端より高い位置となるため、この部位のガスケットの圧縮が行われずガスケットと外装ケースの間に隙間が生じ封口性の改善効果が比較的小さいことも分かった。
【００１８】
また、周縁曲線部の加締め形状は加締め後のケース先端の加締め形状が１／４周以上の弧長を有する曲線、すなわち、曲げ開始点から終点（ケース先端）までの曲げ角度が９０°以上の曲線である形に加締めるのがよい。周縁曲線部の外装ケースは円周方向の圧縮作用が働くため周縁直線部ほどスプリングバックは生じ難く、９０°以上の曲げ角度を有していれば実用に耐える。無理に直線部を有する形状に加締めようとした場合、ガスケットにストレスを与え反って好ましくない。
【００１９】
この場合、曲げ開始点の位置を周縁直線部の曲げ開始点の位置と等しくし、また、曲げ終点の位置を周縁直線部の外装ケース先端の位置に揃えるのがよい。これにより周縁曲線部と周縁直線部の形状差異により両者の境界部分で封口性が劣ることを防止できる。
【００２０】
ここで、本発明は扁平角形電池の封口構造について、詳しくは外装ケースの加締め形状を改良し、封口性を向上することに主点を置いたものであり、電極および電極構成については限定されるものではなく、電極構造については、薄膜電極を捲回した捲回電極の他、薄膜電極を積層した積層電極、顆粒を成形したペレット電極等、あらゆる電極について同様の効果が期待できる。
【００２１】
【発明の実施の形態】
以下、本発明の実施例及び比較例について、リチウムイオン二次電池に採用した場合を例に、詳細に説明する。
【００２２】
（実施例１）
本実施例１の電池の断面図を図１に、平面図を図２にそれぞれ示す。以下本実施例１の電池の製造方法を説明する。
【００２３】
まず、ＬｉＣｏＯ₂１００質量部に対し導電材としてアセチレンブラック５質量部と黒鉛粉末５質量部を加え、結着剤としてポリフッ化ビニリデンを５質量部加え、Ｎ−メチルピロリドンで希釈、混合し、スラリー状の正極合剤を得た。次にこの正極合剤を、正極集電体である厚さ０．０２ｍｍのアルミ箔の片面にドクターブレード法により塗工、乾燥を行い、アルミ箔表面に正極作用物質含有層を形成した。以後、正極作用物質含有層の塗膜厚さが両面で０．１５ｍｍとなるまで塗工、乾燥を繰り返し、両面塗工正極を作製した。次に、この電極体の片面の端から２０ｍｍ部分の作用物質含有層を除去し、アルミ層を剥き出し通電部とし、幅１９ｍｍ、長さ２００ｍｍ、厚さ０．１５ｍｍの長さに切り出した正極板を作製した。
【００２４】
次に、黒鉛化メソフェーズピッチ炭素繊維粉末１００質量部に結着剤としてスチレンブダジエンゴム（ＳＢＲ）とカルボキシメチルセルロース（ＣＭＣ）をそれぞれ２．５質量部を添加し、イオン交換水で希釈、混合し、スラリー状の負極合剤を得た。得られた負極合剤を負極集電体である厚さ０．０２ｍｍの銅箔に作用物質含有層の厚さが０．１５ｍｍとなるように正極の場合と同様に塗工、乾燥を繰り返し実施し両面塗工負極を作製した。次に、この電極体の片面の端から２０ｍｍ部分の作用物質含有層を除去し、銅層を剥き出し通電部とし、幅２０ｍｍ、長さ２００ｍｍ、厚さ０．１５ｍｍの長さに切り出した負極板を作製した。
【００２５】
次に、正負極通電部面を外周巻き終わり側とし、これら正極と負極の間に幅２２ｍｍ、厚さ２５μmのポリエチレン微多孔膜からなるセパレータを介し渦巻状に捲回し、扁平形電池の扁平面に対し水平方向に正負極対向部を持つように一定方向に捲回電極の中心部の空間がなくなるまで加圧した。以上の方法により縦２２ｍｍ、横２２ｍｍの扁平コイル状の電極群３を製作した。
【００２６】
次に板厚０．２５ｍｍのステンレス材からなる内装ケース（負極金属ケース）４の内面に厚さ０．０３ｍｍのステンレス製の金属ネット５を溶接し、絶縁ガスケット６と一体化した。続いて８５℃で１２ｈ乾燥処理を行った電極群３を電極群の片面塗工負極板の未塗工側が前述の金属ネット５に接するように配置し、エチレンカーボネートとメチルエチルカーボネートを体積比１：１の割合で混合した溶媒に支持塩としてＬｉＰＦ₆を１ｍｏｌ／ｌの割合で溶解せしめた非水電解質を注液し、さらに電極群の片面塗工正極板の未塗工側に接するように厚さ０．０３ｍｍのＡｌ製の金属ネット２が内面に溶接された板厚０．２ｍｍのステンレス材の内面に厚さ５０μmのＡｌがクラッド処理された板厚ｔ０．２５ｍｍのクラッド材からなる外装ケース（正極ケース）１を嵌合し、上下反転後、外装ケースに加締め加工を実施し、封口し、厚さ３．２ｍｍ、縦３０ｍｍ、横３０ｍｍの実施例１の扁平角形非水電解質二次電池を製作した。
【００２７】
ここで封口部を加締める方法であるが、下パンチ上にガスケットや電極を内包し内装ケースと嵌合した外装ケースを置き、その内装ケースの上面にナックアウトピンを当てた状態で、電池の外周部と同形状を有する角筒状の開口部を有し、その開口部の上部に外装ケースの先端を一回り小さな開口寸法に加締めるダイ金型を下降させ、外装ケースの先端を加締めた。ただし、この方法は従来の円型電池の製造方法に類似した製造方法であり、外装ケースの加締め部に直線部を設け加締めるためにはダイ金型の開口部の形状を次のようにするとよい。
【００２８】
本発明の如く板厚に対し曲げ半径が比較的小さく、また、先端直線部の形状が短い場合はダイ金型に希望する曲げ半径の１〜２倍の半径を有し、曲げ開始から終点までの曲げ角度が１００°〜１５０°のＲ形状を有する金型を用いる。加締める際に外装ケースの先端がダイ金型の内Ｒの上支点（曲げ角度９０°）を過ぎたところでダイ金型の残りの先端Ｒ部により外装ケース先端を外向きに押し返す応力が働き金型Ｒの進行方向にケース先端が逃げるのを防止する作用が働く。これにより外装ケース先端がダイ金型先端に固定されながら加圧力が働くため、外装ケース先端が逃げず、ダイ金型のＲ開始位置から外装ケースの座屈が起こり、先端と加締め曲げＲ部の間に直線部を有する形状に加締められる。また、加締め加工時に外装ケース先端に強大な圧縮応力が作用するため外装ケースのスプリングバックも抑えられる。
【００２９】
ここで、本実施例１の電池を加締めた際の周縁直線部の加締め部の断面拡大図を図３に、周縁曲線部の加締め部の断面拡大図を図４にそれぞれ示す。電池を下パンチ９上に置き、ナックアウトピン８で電池を加圧した状態でダイ金型７を上方から下降させ、図３、図４に示すように封口部を加締めた。
【００３０】
この際、外装ケースを加締めるダイ金型に縦横３０ｍｍ、４角のＲが６Ｒである開口部を有し、その開口部の上端に内方向への曲げＲ１（カン外Ｒ）を有し、その曲げＲの曲げ半径（金型内Ｒ）Ｒ０が０．６５ｍｍで、曲げＲのＲ開始点からＲ終点までの曲げ角度（金型先端Ｒまでの角度）ω０が１３５°であるダイ金型を用いて加締め加工を行った。なお、Ｐ０はＲ０，ω０の原点（金型Ｒの中心）、Ｐ１はＲ１の原点（カン外Ｒの中心）である。
【００３１】
これにより外装ケースの周縁直線部において、加締め後のケース先端形状が長さ０．５ｍｍの直線となり、先端直線部と側壁部を繋ぐ曲線部の曲げ半径Ｒ１がカン外Ｒで０．５ｍｍであり、ケース先端直線部とケース底面のなす角度θ１が０°であり、また、外装ケースの周縁曲線部において、加締め後のケース先端の加締め形状が曲線であり、曲げ半径Ｒ２がカン外Ｒで０．６５ｍｍであり、Ｒ開始点からＲ終点（ケース先端）までの曲げ角度ω２が１２３°である実施例１の電池を得た。この時、加締め加工時に外装ケース先端がダイ金型の先端で押え付けられながら加締められるため、コーナ部では金型Ｒの中心とカン外Ｒの中心が同一となり、半径もＲ２＝Ｒ０となる形状の電池を得ることができる。
【００３２】
（実施例２）
加締める際に曲げ半径Ｒ０が０．５５ｍｍのダイ金型を用いたこと以外は実施例１と同様に電池を製作し、加締め加工後の外装ケース周縁直線部の曲げ半径Ｒ１が０．３７５ｍｍであり、外装ケース周縁曲線部の曲げ半径Ｒ２が０．５５ｍｍ、曲げ角度ω２が１２６°である以外は実施例１と同様の電池を得た。
【００３３】
（実施例３）
加締める際に曲げ半径Ｒ０が０．８ｍｍのダイ金型を用いたこと以外は実施例１と同様に電池を製作し、加締め加工後の外装ケース周縁直線部の曲げ半径Ｒ１が０．６５ｍｍであり、外装ケース周縁曲線部の曲げ半径Ｒ２が０．８ｍｍ、曲げ角度ω２が１１６°である以外は実施例１と同様の電池を得た。
【００３４】
（実施例４）
加締める際に曲げ半径Ｒ０が０．９５ｍｍのダイ金型を用いたこと以外は実施例１と同様に電池を製作し、加締め加工後の外装ケース周縁直線部の曲げ半径Ｒ１が０．８５ｍｍであり、外装ケース周縁曲線部の曲げ半径Ｒ２が０．９５ｍｍ、曲げ角度ω２が１１５°である以外は実施例１と同様の電池を得た。
【００３５】
（実施例５）
加締める際に曲げ半径Ｒ０が１．１ｍｍのダイ金型を用いたこと以外は実施例１と同様に電池を製作し、加締め加工後の外装ケース周縁直線部の曲げ半径Ｒ１が１ｍｍであり、外装ケース周縁曲線部の曲げ半径Ｒ２が１．１ｍｍ、曲げ角度ω２が１１１°である以外は実施例１と同様の電池を得た。
【００３６】
（比較例１）
加締める際に図５の断面拡大図に示す曲げ半径Ｒ０が１．３ｍｍであり曲げ角度ω０が９０°であるダイ金型を用いたこと以外は実施例１と同様に電池を製作し、外装ケース周縁直線部において、加締め後のケース先端の形状が曲線であり、曲げ半径Ｒ１が外Ｒで１．４ｍｍ、Ｒ開始点から終点（ケース先端）までの曲げ角度ω１が８０°、周縁曲線部の形状が曲げ半径Ｒ２が１．３ｍｍ、曲げ角度ω２が８０°である以外は実施例１と同様の電池を得た。
【００３７】
この比較例１の電池では、周縁直線部の曲げ半径Ｒ１がダイ金型内面の曲げ半径Ｒ０より大きくなっており、外装ケースのスプリングバックにより加締め加工後に戻りがでたものと考えられる。
【００３８】
（比較例２）
加締める際に曲げ角度ω０が９０°であるダイ金型を用いたこと以外は実施例１と同様に電池を製作し、外装ケース周縁直線部において、加締め後のケース先端の形状が曲線であり、曲げ半径Ｒ１が外Ｒで０．７ｍｍ、Ｒ開始点から終点（ケース先端）までの曲げ角度ω１が８０°、周縁曲線部の形状が曲げ半径Ｒ２が０．６５ｍｍ、曲げ角度ω２が８０°である以外は実施例１と同様の電池を得た。この電池の周縁直線部の断面拡大図を図５に示す。
【００３９】
この比較例２の電池では、周縁直線部の曲げ半径Ｒ１がダイ金型内面の曲げ半径Ｒ０より僅かに大きくなっているが、これは外装ケースのスプリングバックにより加締め加工後に戻りがでたものと考えられる。
【００４０】
（参考例１）
加締める際に曲げ半径Ｒ０が０．４３ｍｍのダイ金型を用いたこと以外は実施例１と同様に電池を製作し、加締め加工後の外装ケース周縁直線部の曲げ半径Ｒ１が０．２５ｍｍであり、外装ケース周縁曲線部の曲げ半径Ｒ２が０．４３ｍｍ、曲げ角度ω２が１３８°である以外は実施例１と同様の電池を得た。
【００４１】
（参考例２）
加締める際に曲げ半径Ｒ０が１．３ｍｍのダイ金型を用いたこと以外は実施例１と同様に電池を製作し、加締め加工後の外装ケース周縁直線部の曲げ半径Ｒ１が１．２ｍｍであり、外装ケース周縁曲線部の曲げ半径Ｒ２が１．３ｍｍ、曲げ角度ω２が１０８°である以外は実施例１と同様の電池を得た。
【００４２】
（実施例６）
加締め加工後の外装ケース周縁直線部の曲げＲ部の曲げ角度ω１を６５°、先端直線部とケース底面のなす角度θ１を２５°とした以外は実施例１と同様に電池を作製した。
【００４３】
（実施例７）
加締め加工後の外装ケース周縁直線部の曲げＲ部の曲げ角度ω１を７５°、先端直線部とケース底面のなす角度θ１を１５°とした以外は実施例１と同様に電池を作製した。
【００４４】
（実施例８）
加締め加工後の外装ケース周縁直線部の曲げＲ部の曲げ角度ω１を１０５°、先端直線部とケース底面のなす角度θ１を−１５°とした以外は実施例１と同様に電池を作製した。
【００４５】
（参考例３）
加締め加工後の外装ケース周縁直線部の曲げＲ部の曲げ角度ω１を５５°、先端直線部とケース底面のなす角度θ１を３５°とした以外は実施例１と同様に電池を作製した。
【００４６】
（参考例４）
加締め加工後の外装ケース周縁直線部の曲げＲ部の曲げ角度ω１を１１５°、先端直線部とケース底面のなす角度θ１を−２５°とした以外は実施例１と同様に電池を作製した。
【００４７】
以上の通り、本実施例１〜８、比較例１，２及び参考例１〜４の電池を各１００個製作した。電池の外観検査を実施し外観不良率を算出した。その後、４．２Ｖ、１０ｍＡの定電流定電圧で４８ｈ初充電を実施し、３日間室温で放置後、７０℃−９３％ＲＨの雰囲気下で３０日間保存し、保存後の電池の開路電圧と保存試験前に対する電池の総高増加量を測定した。保存後の電池の開路電圧が３．８Ｖ以下のものを開路電圧不具合品とし、また、電池総高の増加量が０．５ｍｍ以上のものを電池総高不具合品と判定し、それぞれの発生率を集計した。また試験後の電池２０個を抜き取り、それらの電池を分解し、内装ケースを取出し、内装ケース側壁の電池中心部に向けての湾曲量を測定した。その測定結果を表１に示す。
【００４８】
【表１】

【００４９】
本発明の実施例の電池は先に述べた通り、外装ケースに生じるスプリングバック量が少なく、また、表１より明らかであるが内装ケースの湾曲量も少ない。その結果、高温高湿下に保存しても電池内への水分の浸入が少なく開路電圧低下品の発生率は極めて低く、また電池の膨れも起こり難い。周縁直線部の外装ケースの先端加締め形状が従来にみられた円弧状の形状となっている比較例１及び比較例２の電池は内装ケースの湾曲量が極端に大きく封口性に劣る。先端加締め形状が直線状になっている本実施例及び参考例の電池と比較するとその効果は明らかである。
【００５０】
また、外装ケース周縁直線部の曲げ半径Ｒ１が基材板厚と同様の参考例１の電池と水平角度θ１が小さい参考例４の電池では製作直後に外観不良の発生が見られるが、前者は加締め曲げ部に傷が生じたもので、後者は負極ケースの周縁部が過度に押し下げられたことにより負極ケースの平坦部に歪みが生じたものである。
【００５１】
また、加締め曲げ半径の大きな参考例２の電池は封口性が若干劣るが、こちらは内装ケースの湾曲が本実施例の電池に比べ若干大きく、周縁直線部の封口性が劣ったものと考えられる。
【００５２】
さらに、水平角度θ１が大きな参考例３では内装ケースの湾曲は小さいが封口性が若干劣り、保存期間中に外装ケース先端の加締めが甘くなったものと考えられる。
【００５３】
また水平角度θ１が小さい参考例４の電池では、電池製作後に電池の封口部の断面形状を確認したところ加締め曲げ部のガスケットと外装ケースの間に微小な隙間が生じているのが確認された。そのため保存時の封口性が若干低下したものと考えられる。
【００５４】
次に、電池サイズを縦２０ｍｍ、横２０ｍｍに変更し表１と同様の測定を行い、その結果について述べる。
【００５５】
（実施例９）
負極ケースの基材を厚さ０．２ｍｍのステンレス材とし、正極ケースの基材を厚さ０．１５ｍｍのステンレス材の内面に厚さ５０μmのアルミをクラッド処理した厚さｔ０．２ｍｍのクラッド材とし、用いた電極群の寸法を縦１３ｍｍ、横１３ｍｍの扁平コイル状とした以外は実施例１の場合と同様に厚さ３．１ｍｍ、縦２０ｍｍ、横２０ｍｍの扁平角形非水電解質二次電池を製作した。
【００５６】
この際、外装ケースを加締めるダイ金型に縦横２０ｍｍ、４角のＲが４．８Ｒである開口部を有し、その開口部の上端に内方向への曲げＲを有し、その曲げＲの曲げ半径Ｒ０が０．５ｍｍで、曲げＲのＲ開始点からＲ終点までの曲げ角度ω０が１３５°であるダイ金型を用いて加締め加工を行った。
【００５７】
これにより外装ケースの周縁直線部において、加締め後のケース先端形状が長さ０．４ｍｍの直線となり、先端直線部と側壁部を繋ぐ曲線部の曲げ半径Ｒ１が外Ｒで０．４ｍｍ、ケース先端直線部とケース底面のなす角度θ１が０°、また、外装ケースの周縁曲線部において、加締め後のケース先端の加締め形状が曲線であり、曲げ半径Ｒ２が外Ｒで０．５ｍｍ、Ｒ開始点からＲ終点までの曲げ角度ω２が１２３°である実施例９の電池を得た。
【００５８】
（実施例１０）
加締める際に曲げ半径Ｒ０が０．４５ｍｍのダイ金型を用いたこと以外は実施例９と同様に電池を製作し、加締め加工後の外装ケース周縁直線部の曲げ半径Ｒ１が０．３ｍｍであり、外装ケース周縁曲線部の曲げ半径Ｒ２が０．４５ｍｍ、曲げ角度ω２が１２６°である以外は実施例９と同様の電池を得た。
【００５９】
（実施例１１）
加締める際に曲げ半径Ｒ０が０．６５ｍｍのダイ金型を用いたこと以外は実施例１と同様に電池を製作し、加締め加工後の外装ケース周縁直線部の曲げ半径Ｒ１が０．５ｍｍであり、外装ケース周縁曲線部の曲げ半径Ｒ２が０．６５ｍｍ、曲げ角度ω２が１１６°である以外は実施例９と同様の電池を得た。
【００６０】
（実施例１２）
加締める際に曲げ半径Ｒ０が０．７５ｍｍのダイ金型を用いたこと以外は実施例１と同様に電池を製作し、加締め加工後の外装ケース周縁直線部の曲げ半径Ｒ１が０．７ｍｍであり、外装ケース周縁曲線部の曲げ半径Ｒ２が０．７５ｍｍ、曲げ角度ω２が１１５°である以外は実施例９と同様の電池を得た。
【００６１】
（実施例１３）
加締める際に曲げ半径Ｒ０が０．９ｍｍのダイ金型を用いたこと以外は実施例１と同様に電池を製作し、加締め加工後の外装ケース周縁直線部の曲げ半径Ｒ１が０．８ｍｍであり、外装ケース周縁曲線部の曲げ半径Ｒ２が０．９ｍｍ、曲げ角度ω２が１１１°である以外は実施例９と同様の電池を得た。
【００６２】
（比較例３）
加締める際に曲げ角度ω０が９０°であるダイ金型を用いたこと以外は実施例９と同様に電池を製作し、外装ケース周縁直線部において、加締め後のケース先端の形状が曲線であり、曲げ半径Ｒ１が外Ｒで０．６ｍｍ、Ｒ開始点から終点（ケース先端）までの曲げ角度ω１が８０°、周縁曲線部の形状が曲げ半径Ｒ２が０．５ｍｍ、曲げ角度ω２が８０°である以外は実施例９と同様の電池を得た。
【００６３】
ここで周縁直線部の曲げ半径Ｒ１がダイ金型内面の曲げ半径Ｒ０より僅かに大きくなっているが、これは外装ケースのスプリングバックにより加締め加工後に戻りがでたものと考えられる。
【００６４】
（参考例５）
加締める際に曲げ半径Ｒ０が０．３５ｍｍのダイ金型を用いたこと以外は実施例９と同様に電池を製作し、加締め加工後の外装ケース周縁直線部の曲げ半径Ｒ１が０．２ｍｍであり、外装ケース周縁曲線部の曲げ半径Ｒ２が０．３５ｍｍ、曲げ角度ω２が１３８°である以外は実施例９と同様の電池を得た。
【００６５】
（参考例６）
加締める際に曲げ半径Ｒ０が１．０５ｍｍのダイ金型を用いたこと以外は実施例９と同様に電池を製作し、加締め加工後の外装ケース周縁直線部の曲げ半径Ｒ１が０．９５ｍｍであり、外装ケース周縁曲線部の曲げ半径Ｒ２が１．０５ｍｍ、曲げ角度ω２が１０８°である以外は実施例９と同様の電池を得た。
【００６６】
以上の通り、本実施例９〜１３、比較例３、及び参考例５，６の電池を各１００個製作した。電池の外観不良率、７０℃−９３％ＲＨ３０日保存後の開路電圧不具合品と電池総高不具合品の発生率、及び試験後の電池２０個の抜取り調査による内装ケース側壁の湾曲量を測定し、その結果を表２に示す。
【００６７】
【表２】

【００６８】
電池サイズ及び正負極ケースの板厚が異なる場合でも、先に示した縦横３０ｍｍの電池の場合とほぼ同様の結果が得られた。
なお、本発明の実施例は、非水電解質に非水溶媒を用いた扁平形非水溶媒二次電池を用いて、正極ケースを外装ケースとした場合の加締め加工により封口する扁平角型電池をもとに説明したが、正負極電極を入れ替え、外装ケースとして負極ケースを配置することも可能である。さらに、他の電池系への適用も可能であり、扁平角型の加締め封口については同様の効果が得られる。
【００６９】
【発明の効果】
以上説明したとおり、本発明によれば加締め封口時の外装ケース周縁直線部に生じるスプリングバックと内装ケースに生じる変形を防止し、封口性を向上することができるので、工業的価値の非常に大きな扁平角型電池を提供することができる。
【図面の簡単な説明】
【図１】本発明の実施例１の電池の断面図。
【図２】本発明の実施例１の電池の平面図。
【図３】本発明の実施例１の電池の周縁直線部の封口部断面拡大図。
【図４】本発明の実施例１の電池の周縁曲線部の封口部断面拡大図。
【図５】比較例の電池の周縁直線部の封口部断面拡大図。
【符号の説明】
１…外装ケース（正極ケース）、２…正極集電体、３…扁平渦巻き状電極群、４…内装ケース（負極ケース）、５…負極集電体、６…絶縁ガスケット、７…本発明のダイ金型、８…ナックアウトピン、９…下パンチ、10…従来例のダイ金型、Ａ…周縁曲線部、Ｂ…周縁直線部。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a flat battery, and more particularly to a flat battery having a spring back generated in an outer case and a deformation of the inner case to improve sealing performance.
[0002]
[Prior art]
Downsizing of devices used has been accelerating mainly on small information terminals such as mobile phones and PDAs, and secondary batteries as a main power source are also required to be downsized. On the other hand, a metal negative electrode case also serving as a negative electrode terminal as shown in Patent Document 1 and Patent Document 2 and a metal positive electrode case also serving as a positive electrode terminal are fitted via an insulating gasket, and the positive electrode case or A flat non-aqueous electrolyte secondary battery having a sealing structure in which a negative electrode case is crimped by caulking and includes a non-aqueous electrolyte and a power generation element including at least a positive electrode, a separator, and a negative electrode. When a cross section in a direction perpendicular to the flat surface of the battery is viewed, an electrode group having positive and negative electrode facing surfaces in which at least three or more positive and negative electrodes are opposed to each other via a separator is housed, and within the electrode group A flat non-aqueous electrolyte secondary battery in which the sum of the positive and negative electrode facing areas is larger than the opening area of the insulating gasket has been proposed as a battery that satisfies the demand for miniaturization.
[0003]
[Patent Document 1]
JP 2001-068160 A
[Patent Document 2]
JP 2001-068143 A
[0004]
In addition, recently, small devices having a display device such as a liquid crystal display have been made thinner, but the size of the display device has an upper limit of actual use, so the ratio of the occupied area of the display device to the entire device is reduced. Increasing the size of the device as much as possible and reducing the size of the entire device is under consideration. Since many of these display devices have a square shape, in order to match the device to this shape, many devices have a square shape as a whole. There is a demand for a small flat battery typified by a square or oval shape having two or more straight portions and the ends of each straight portion being connected by a substantially arcuate curved portion.
[0005]
However, in the case of a battery in which a sealing plate is sealed by laser welding to a deeply drawn outer case as seen in conventional Li ion or nickel metal hydride secondary batteries, assembly processes such as making thin cans and inserting electrodes Due to the above limitations, the battery size is almost reached.
[0006]
Therefore, a battery with a new sealing structure is required to produce a smaller and thin battery having a substantially square shape, and an insulating gasket is interposed between the metal outer case and the inner case with the electrodes held inside. A battery that is fitted and further has a sealing part formed by crimping the outer case is desirable.
[0007]
However, when a flat rectangular battery having a straight edge portion is crimped to an arc of 1/8 to 1/4 as in the case of a conventional coin-shaped or button-shaped battery, the straight edge portion of the outer case As a result, spring back was generated and the sealing became sweet, or when the exterior case was crimped, the side wall of the interior case was inwardly inclined or curved, and sufficient sealing performance could not be obtained. In particular, when the battery is stored under high temperature and high humidity with a high vapor pressure, it will be greatly affected, and moisture (water vapor) will enter the battery from the outside, greatly reducing the open circuit voltage of the battery or causing gas generation. The battery was swollen. The former reduces the basic function of the battery as a power source, and the latter causes the battery to swell out of the standard size and deforms or damages the thinned equipment, so that improvement has been desired.
[0008]
In the case of a conventional coin-type or button-type battery, if the inner case is inclined inward, the radius of the opening of the inner case is reduced, so that a uniform compressive stress acts on the case base material in the circumferential direction. . Since the action of the beam repelling this acts on the interior case, it is difficult for the interior case of the circular interior case to be inclined or bent (depressed). However, in a battery having a peripheral straight portion, the peripheral curved portion acts like a beam as in the conventional circular battery, but the peripheral straight portion is substantially close to a bent plate. The action did not work, the proof stress was weak against the compressive stress acting when caulking the exterior case, and the inner case side wall was inclined or curved. As a result, the expected sealing performance cannot be obtained, and when the caulking pressure of the outer case is weakened to prevent the inner case from being bent, the gasket compression rate decreases and the outer case spring back. The desired sealing performance could not be obtained.
[0009]
[Problems to be solved by the invention]
The present invention has been made in order to cope with the above situation, and its problem is to prevent inward tilting and bending of the inner case during the caulking process of the outer case and spring back generated in the outer case after caulking, and An object of the present invention is to provide a flat rectangular battery in which the strength of the sealing portion is increased, the open circuit voltage is hardly lowered even when the battery is placed under high temperature and high humidity, and the total battery height is little increased.
[0010]
[Means for Solving the Problems]
As a result of intensive research, the present inventors have found that the metal outer case and the metal inner case are fitted to the flat surface of the battery through the insulating gasket in the vertical direction, and further on the outer peripheral side of the insulating gasket. The arranged outer case has a sealing structure that is crimped by crimping, and the thickness of the battery is smaller than the outer dimension, and at least two peripheral linear portions (hereinafter referred to as peripheral linear portions) B), and each end portion of the linear portion is connected by a peripheral curved portion (hereinafter referred to as a peripheral curved portion A), The caulking shape of the peripheral curve portion is a curve, The exterior case at a portion corresponding to the peripheral straight line portion is crimped into a shape in which a straight portion is provided between the front end of the exterior case and the crimped bending portion. It has been found that inward tilting and curving and springback that occurs in the outer case are prevented, the sealing strength is increased, and the ingress of moisture from the outside can be prevented even when the battery is placed under high temperature and high humidity.
[0011]
As a result of analysis by paying attention to the caulking behavior of the outer case, the present inventors added a shape having a 1/8 to 1/4 arc with the front end of the outer case facing inward as in the conventional circular battery. When tightening, the side wall of the exterior case once inclines excessively from the periphery of the bottom of the case in the process of crimping at the peripheral straight portion, and then bends into a shape that conforms to the R shape of the crimping mold. I found out. For this reason, it was found that the outer case side wall that collapsed from the bottom of the side wall in the intermediate process of crimping pressed the inner case and the insulating gasket, leading to inward tilting and bending of the inner case side wall.
[0012]
As a result of examining various measures to improve the present inventors, the caulking shape of the outer case is changed from the conventional round shape having an arc of 1/8 to 1/4 over the entire shoulder R portion of the battery. It is possible to prevent the deformation that has occurred in the interior case by changing the shape of the caulking bend R to a shape that is connected as a smaller arc than in the past by forming a straight part between the tip of the outer case and the caulking bend R. I found it.
[0013]
In addition, since the bending load is concentrated near the center of the outer case side wall, which is the end of the straight line, because the outer case has a shape with a straight line portion, the outer case can be caulked so that it can be easily bent from the center of the side wall. it can. Since the folding fulcrum moves from the bottom of the case side wall to the center of the side wall, the amount of movement that the case tip moves inward is reduced, and the pressing pressure that the outer case side wall applies to the gasket side and the inner case inside it can be reduced. As a result, deformation of the interior case can be prevented.
[0014]
Furthermore, the hardness of the sealing portion can be improved by bending the center of the side wall, and excellent sealing properties can be maintained over a long period of time. At this time, it is particularly preferable that the bending radius of the caulking bending portion connected to the straight portion provided in the outer case is not more than four times the outer case base plate thickness at the outer R, and the caulking is reduced by reducing the bending radius. The bending load concentrates on the bent portion, and the exterior case can be easily bent from the vicinity of the center of the side wall, and the effect of preventing the inward inclination of the side wall from the bottom of the case can be further enhanced. Furthermore, the smaller the bending radius, the larger the distortion generated in the bent portion, so that subsequent springback hardly occurs.
[0015]
In a conventional round battery, sealing performance is improved by increasing the bending radius at the front end of the outer case because the compression rate of the gasket is increased. Usually, the outer case is adopted with a bending radius 5 to 6 times the plate thickness. The tip is caulked in an arc shape of 1/8 to 1/4 round. In this respect, the battery of the present invention having the peripheral straight portion is greatly different from the conventional circular battery.
[0016]
However, in the battery of the present invention, since the bending radius at which the caulking bending radius is less than 1.5 times the thickness of the base material is too small, fine scratches are likely to occur on the metal case surface and the mold surface of the caulking bending portion. The appearance of the finished battery may be inferior, and the bending radius is more preferably 1.5 times the thickness of the base material.
[0017]
Next, the inventors noticed that the strength of the sealing portion was improved by caulking with leaving the straight part in the outer case, and examined the bending angle of the straight part provided in the outer case after caulking. Piled up. As a result, the straightened portion after caulking is substantially orthogonal to the side wall of the outer case, and the straight portion provided on the outer case is kept in a horizontal angle range of 25 ° to −15 ° with respect to the bottom surface of the outer case. It has been found that it is extremely strong against stress and warping of the case base material, and even when the battery is placed in a severe external environment, the sealing part is hardly deformed, and moisture can be prevented from entering from the outside over a long period of time. . On the other hand, if the horizontal angle is smaller than −15 °, the end of the straight portion of the exterior case excessively pushes down the overhanging portion of the interior case, causing the interior case to be deformed, or the caulking bending portion at the center of the exterior case. Since the position is higher than the front end of the outer case, it was also found that the gasket at this portion was not compressed and a gap was formed between the gasket and the outer case, and the sealing effect was relatively small.
[0018]
Further, the caulking shape of the peripheral curve portion is a curve in which the caulking shape of the case tip after caulking has an arc length of ¼ or more, that is, the bending angle from the bending start point to the end point (case tip) is 90. It is better to caulk in a shape that is a curve of more than °. Since the outer peripheral case of the peripheral curve portion has a compressive action in the circumferential direction, the spring back is less likely to occur in the linear peripheral portion, and it can be practically used if it has a bending angle of 90 ° or more. If it is forced to caulk in a shape having a straight portion, stress is applied to the gasket, which is not preferable.
[0019]
In this case, it is preferable that the position of the bending start point is made equal to the position of the bending start point of the peripheral straight line portion, and the position of the bending end point is aligned with the position of the outer case front end of the peripheral straight line portion. Thereby, it can prevent that sealing performance is inferior in the boundary part of both by the shape difference of a periphery curve part and a periphery straight line part.
[0020]
Here, the present invention focuses on the sealing structure of a flat rectangular battery, in particular, by improving the caulking shape of the outer case and improving the sealing performance, and the electrode and the electrode configuration are limited. As for the electrode structure, the same effect can be expected for all electrodes such as a wound electrode obtained by winding a thin film electrode, a laminated electrode obtained by laminating thin film electrodes, and a pellet electrode obtained by forming granules.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, examples and comparative examples of the present invention will be described in detail, taking as an example the case of being adopted in a lithium ion secondary battery.
[0022]
Example 1
A sectional view of the battery of Example 1 is shown in FIG. 1, and a plan view thereof is shown in FIG. A method for manufacturing the battery of Example 1 will be described below.
[0023]
First, LiCoO ₂ Add 100 parts by mass of 5 parts by mass of acetylene black and 5 parts by mass of graphite powder as a conductive material, add 5 parts by mass of polyvinylidene fluoride as a binder, dilute and mix with N-methylpyrrolidone, and mix the slurry positive electrode composition. An agent was obtained. Next, this positive electrode mixture was applied to one side of a 0.02 mm thick aluminum foil serving as a positive electrode current collector by a doctor blade method and dried to form a positive electrode active substance-containing layer on the aluminum foil surface. Thereafter, coating and drying were repeated until the coating film thickness of the positive electrode active material-containing layer became 0.15 mm on both sides, to produce a double-sided coated positive electrode. Next, the active substance-containing layer of the 20 mm portion is removed from one end of the electrode body, the aluminum layer is stripped to form a current-carrying portion, and a positive electrode plate cut out to a length of 19 mm in width, 200 mm in length, and 0.15 mm in thickness. Was made.
[0024]
Next, 2.5 parts by mass of styrene budadiene rubber (SBR) and carboxymethyl cellulose (CMC) as a binder are added to 100 parts by mass of graphitized mesophase pitch carbon fiber powder, respectively, diluted with ion-exchanged water, mixed, A slurry-like negative electrode mixture was obtained. The obtained negative electrode mixture was repeatedly applied and dried in the same manner as in the case of the positive electrode so that the thickness of the active substance-containing layer was 0.15 mm on a 0.02 mm thick copper foil as a negative electrode current collector. A double-sided coated negative electrode was produced. Next, the 20 mm portion of the active substance-containing layer is removed from the end of one side of the electrode body, the copper layer is stripped to form a current-carrying portion, and a negative electrode plate cut into a length of 20 mm in width, 200 mm in length, and 0.15 mm in thickness. Was made.
[0025]
Next, the positive and negative electrode energization part surface is the outer winding end side, and the coil is wound between the positive electrode and the negative electrode through a separator made of a polyethylene microporous film having a width of 22 mm and a thickness of 25 μm. On the other hand, pressure was applied in a certain direction so as to have a positive and negative electrode facing portion in the horizontal direction until there was no space in the center of the wound electrode. The flat coiled electrode group 3 having a length of 22 mm and a width of 22 mm was manufactured by the above method.
[0026]
Next, a stainless steel metal net 5 having a thickness of 0.03 mm was welded to the inner surface of an interior case (negative electrode metal case) 4 made of a stainless steel material having a thickness of 0.25 mm and integrated with the insulating gasket 6. Subsequently, the electrode group 3 subjected to a drying treatment at 85 ° C. for 12 hours is arranged so that the uncoated side of the single-side coated negative electrode plate of the electrode group is in contact with the metal net 5 described above, and ethylene carbonate and methyl ethyl carbonate are in a volume ratio of 1 LiPF as a supporting salt in a solvent mixed at a ratio of 1 ₆ A non-aqueous electrolyte in which 1 mol / l is dissolved is injected, and an Al metal net 2 having a thickness of 0.03 mm is formed on the inner surface so as to be in contact with the uncoated side of the single-side coated positive electrode plate of the electrode group. An outer case (positive electrode case) 1 made of a clad material having a thickness of 0.25 mm and clad with 50 μm thickness of aluminum is fitted on the inner surface of a stainless steel material having a thickness of 0.2 mm welded to the plate, and then turned upside down. The outer case was crimped and sealed to produce a flat rectangular nonaqueous electrolyte secondary battery of Example 1 having a thickness of 3.2 mm, a length of 30 mm, and a width of 30 mm.
[0027]
This is a method of crimping the sealing part. Place an outer case that contains a gasket or electrode on the lower punch and is fitted with the inner case, and with the nack-out pin applied to the upper surface of the inner case, A square cylinder-shaped opening having the same shape as the outer periphery, and a die mold that crimps the tip of the outer case to a small opening size is lowered above the opening, and the tip of the outer case is crimped It was. However, this method is a manufacturing method similar to the manufacturing method of the conventional circular battery, and the shape of the opening of the die mold is set as follows in order to provide a straight portion in the caulking portion of the outer case and perform caulking. Good.
[0028]
When the bending radius is relatively small with respect to the plate thickness as in the present invention and the shape of the straight end portion is short, the die mold has a radius that is 1 to 2 times the desired bending radius, from the start to the end of bending. A mold having an R shape with a bending angle of 100 ° to 150 ° is used. When the end of the outer case passes over the upper fulcrum (bending angle 90 °) of the inside of the die mold when caulking, the remaining tip R of the die mold pushes the outer case tip outward to work the die. The action of preventing the case tip from escaping in the direction of travel of the mold R works. As a result, pressure is applied while the outer case tip is fixed to the die die tip, so the outer case tip does not escape, buckling of the outer case occurs from the R start position of the die die, and the tip and caulking bending R portion. It is crimped to the shape which has a linear part between. Further, since a strong compressive stress acts on the front end of the outer case during the caulking process, the spring back of the outer case can be suppressed.
[0029]
Here, FIG. 3 shows an enlarged cross-sectional view of the caulking portion of the peripheral straight portion when the battery of Example 1 is caulked, and FIG. 4 shows an enlarged cross-sectional view of the caulked portion of the peripheral curved portion. The battery was placed on the lower punch 9, the die mold 7 was lowered from above in a state where the battery was pressurized with the knuckle pin 8, and the sealing portion was crimped as shown in FIGS. 3 and 4.
[0030]
At this time, the die mold for caulking the outer case has an opening with a length and width of 30 mm, a square R of 6R, and has an inward bending R1 (outside R) at the upper end of the opening, A die mold in which the bending radius (in-mold R) R0 of the bending R is 0.65 mm, and the bending angle (angle to the mold tip R) ω0 of the bending R from the R start point to the R end point is 135 °. The caulking process was performed using Note that P0 is the origin of R0 and ω0 (center of the mold R), and P1 is the origin of R1 (center of R outside the can).
[0031]
As a result, the case tip shape after caulking becomes a straight line with a length of 0.5 mm at the straight edge portion of the outer case, and the bending radius R1 of the curved portion connecting the straight tip portion and the side wall portion is 0.5 mm outside the can. Yes, the angle θ1 formed between the case tip straight line portion and the case bottom is 0 °, and the caulking shape of the case tip after caulking is a curve in the peripheral curve portion of the outer case, and the bending radius R2 is outside the can The battery of Example 1 was obtained, in which R was 0.65 mm and the bending angle ω2 from the R start point to the R end point (case tip) was 123 °. At this time, since the tip of the outer case is clamped while being pressed by the tip of the die mold during the crimping process, the center of the mold R and the center of the outer can R are the same at the corner, and the radius is also R2 = R0. A battery having the following shape can be obtained.
[0032]
(Example 2)
A battery was manufactured in the same manner as in Example 1 except that a die mold having a bending radius R0 of 0.55 mm was used for crimping, and the bending radius R1 of the outer case peripheral straight portion after crimping was 0.375 mm. A battery similar to that of Example 1 was obtained except that the bending radius R2 of the outer peripheral edge curve portion was 0.55 mm and the bending angle ω2 was 126 °.
[0033]
(Example 3)
A battery was manufactured in the same manner as in Example 1 except that a die mold having a bending radius R0 of 0.8 mm was used for crimping, and the bending radius R1 of the outer case peripheral straight portion after crimping was 0.65 mm. A battery similar to that of Example 1 was obtained except that the bending radius R2 of the outer peripheral edge curve portion was 0.8 mm and the bending angle ω2 was 116 °.
[0034]
Example 4
A battery was manufactured in the same manner as in Example 1 except that a die mold having a bending radius R0 of 0.95 mm was used for crimping, and the bending radius R1 of the outer case peripheral straight portion after crimping was 0.85 mm. A battery similar to that of Example 1 was obtained except that the bending radius R2 of the outer peripheral case peripheral curve portion was 0.95 mm and the bending angle ω2 was 115 °.
[0035]
(Example 5)
A battery was manufactured in the same manner as in Example 1 except that a die mold having a bending radius R0 of 1.1 mm was used for crimping, and the bending radius R1 of the outer case straight edge portion after crimping was 1 mm. A battery similar to that of Example 1 was obtained except that the bending radius R2 of the outer case peripheral curve portion was 1.1 mm and the bending angle ω2 was 111 °.
[0036]
(Comparative Example 1)
A battery was manufactured in the same manner as in Example 1 except that a die mold having a bending radius R0 of 1.3 mm and a bending angle ω0 of 90 ° shown in the enlarged cross-sectional view of FIG. In the case peripheral straight part, the shape of the case tip after caulking is a curve, the bending radius R1 is 1.4 mm at the outer R, the bending angle ω1 from the R start point to the end point (case tip) is 80 °, and the peripheral curve A battery similar to that of Example 1 was obtained except that the shape of the part was 1.3 mm in bending radius R2 and 80 ° in bending angle ω2.
[0037]
In the battery of Comparative Example 1, the bending radius R1 of the peripheral straight line portion is larger than the bending radius R0 of the inner surface of the die mold, and it is considered that the battery case was returned after caulking by the spring back of the outer case.
[0038]
(Comparative Example 2)
A battery was manufactured in the same manner as in Example 1 except that a die mold having a bending angle ω0 of 90 ° was used for caulking, and the shape of the case tip after caulking was a curved line at the outer peripheral case peripheral straight part. Yes, the bending radius R1 is 0.7 mm at the outer R, the bending angle ω1 from the R start point to the end point (case tip) is 80 °, the shape of the peripheral curved portion is the bending radius R2 is 0.65 mm, and the bending angle ω2 is 80 A battery was obtained in the same manner as in Example 1 except for the temperature. FIG. 5 shows an enlarged cross-sectional view of the peripheral straight line portion of the battery.
[0039]
In the battery of Comparative Example 2, the bending radius R1 of the peripheral straight line portion is slightly larger than the bending radius R0 of the inner surface of the die mold, but this was returned after caulking by the spring back of the outer case. it is conceivable that.
[0040]
(Reference Example 1)
A battery was produced in the same manner as in Example 1 except that a die mold having a bending radius R0 of 0.43 mm was used for crimping, and the bending radius R1 of the outer case straight edge portion after crimping was 0.25 mm. A battery similar to that of Example 1 was obtained except that the bending radius R2 of the outer peripheral edge curve portion was 0.43 mm and the bending angle ω2 was 138 °.
[0041]
(Reference Example 2)
A battery was manufactured in the same manner as in Example 1 except that a die mold having a bending radius R0 of 1.3 mm was used for crimping, and the bending radius R1 of the outer case peripheral straight portion after crimping was 1.2 mm. A battery similar to that of Example 1 was obtained except that the bending radius R2 of the outer case peripheral curve portion was 1.3 mm and the bending angle ω2 was 108 °.
[0042]
(Example 6)
A battery was fabricated in the same manner as in Example 1 except that the bend angle ω1 of the bend R portion of the outer case straight edge portion after the crimping process was 65 °, and the angle θ1 formed by the tip straight portion and the case bottom was 25 °.
[0043]
(Example 7)
A battery was fabricated in the same manner as in Example 1 except that the bending angle ω1 of the bending portion R of the outer peripheral straight portion of the outer case after crimping was 75 °, and the angle θ1 formed by the front straight portion and the case bottom was 15 °.
[0044]
(Example 8)
A battery was fabricated in the same manner as in Example 1 except that the bending angle ω1 of the bending R portion of the outer case peripheral straight portion after the caulking process was 105 °, and the angle θ1 formed by the tip straight portion and the case bottom was −15 °. .
[0045]
(Reference Example 3)
A battery was fabricated in the same manner as in Example 1 except that the bending angle ω1 of the bending R portion of the outer peripheral straight portion of the outer case after caulking was set to 55 °, and the angle θ1 formed by the tip straight portion and the case bottom was set to 35 °.
[0046]
(Reference Example 4)
A battery was fabricated in the same manner as in Example 1 except that the bending angle ω1 of the bending portion R of the outer peripheral straight portion of the outer case after crimping was 115 °, and the angle θ1 formed by the straight end portion of the case and the bottom of the case was −25 °. .
[0047]
As described above, 100 batteries of Examples 1 to 8, Comparative Examples 1 and 2, and Reference Examples 1 to 4 were manufactured. The appearance inspection of the battery was performed and the appearance defect rate was calculated. After that, the battery was first charged for 48 hours at a constant current and a constant voltage of 4.2 V, 10 mA, left at room temperature for 3 days, and then stored for 30 days in an atmosphere of 70 ° C.-93% RH. The total height increase of the battery before the storage test was measured. A battery whose open circuit voltage after storage is 3.8 V or less is regarded as a defective open circuit voltage, and a battery whose increase in total battery height is 0.5 mm or more is determined as a defective battery high defective product. Were tabulated. Further, 20 batteries after the test were taken out, the batteries were disassembled, the interior case was taken out, and the amount of bending toward the center of the battery on the side wall of the interior case was measured. The measurement results are shown in Table 1.
[0048]
[Table 1]

[0049]
As described above, the battery of the embodiment of the present invention has a small amount of springback generated in the outer case, and as is clear from Table 1, the amount of bending of the inner case is also small. As a result, even when stored at high temperature and high humidity, the infiltration of moisture into the battery is small, the incidence of open circuit voltage drop products is extremely low, and the battery is unlikely to swell. The batteries of Comparative Example 1 and Comparative Example 2 in which the front end crimped shape of the outer case at the peripheral straight line portion is an arc shape that has been seen in the past have an extremely large amount of curve of the inner case and are inferior in sealing performance. The effect is obvious when compared with the batteries of the present example and the reference example in which the tip caulking shape is linear.
[0050]
In addition, in the battery of Reference Example 1 in which the bending radius R1 of the outer peripheral case peripheral straight portion is the same as the base plate thickness and the battery of Reference Example 4 in which the horizontal angle θ1 is small, appearance defects are observed immediately after manufacture. The caulking bending portion is damaged, and the latter is a case where the flat portion of the negative electrode case is distorted by excessively pressing down the peripheral edge portion of the negative electrode case.
[0051]
In addition, the battery of Reference Example 2 having a large caulking bending radius is slightly inferior in sealing property, but this is considered that the curvature of the interior case is slightly larger than that of the battery in this example and the sealing property of the peripheral straight portion is inferior. It is done.
[0052]
Further, in Reference Example 3 in which the horizontal angle θ1 is large, it is considered that the inner case has a small curve but the sealing property is slightly inferior, and the outer case tip is swaged during the storage period.
[0053]
In the battery of Reference Example 4 having a small horizontal angle θ1, the cross-sectional shape of the sealing portion of the battery was confirmed after the battery was manufactured. It was. Therefore, it is considered that the sealing performance during storage is slightly lowered.
[0054]
Next, the battery size is changed to 20 mm length and 20 mm width, the same measurement as in Table 1 is performed, and the result is described.
[0055]
Example 9
The base material of the negative electrode case is made of stainless steel with a thickness of 0.2 mm, and the base material of the positive electrode case is made of clad material with a thickness of t0.2 mm obtained by clad 50 μm thick aluminum on the inner surface of a stainless steel material with a thickness of 0.15 mm. A flat rectangular non-aqueous electrolyte secondary battery having a thickness of 3.1 mm, a length of 20 mm, and a width of 20 mm is the same as in the case of Example 1 except that the dimensions of the used electrode group are a flat coil shape having a length of 13 mm and a width of 13 mm. Was made.
[0056]
At this time, the die mold for caulking the exterior case has an opening portion having a length and width of 20 mm, a square R of 4.8R, an inward bending R at the upper end of the opening portion, and the bending R Caulking was performed using a die mold having a bending radius R0 of 0.5 mm and a bending angle ω0 from the R start point to the R end point of the bending R of 135 °.
[0057]
As a result, the case tip shape after caulking becomes a straight line having a length of 0.4 mm in the straight edge portion of the outer case, and the bending radius R1 of the curved portion connecting the straight tip portion and the side wall portion is 0.4 mm at the outer R. The angle θ1 formed between the straight end portion of the tip and the bottom surface of the case is 0 °, and in the peripheral curved portion of the exterior case, the crimped shape of the case tip after crimping is a curve, the bending radius R2 is 0.5 mm at the outer radius R, A battery of Example 9 was obtained in which the bending angle ω2 from the R start point to the R end point was 123 °.
[0058]
(Example 10)
A battery was manufactured in the same manner as in Example 9 except that a die mold having a bending radius R0 of 0.45 mm was used for crimping, and the bending radius R1 of the outer case peripheral straight portion after crimping was 0.3 mm. A battery similar to that of Example 9 was obtained except that the bend radius R2 of the outer case peripheral curve portion was 0.45 mm and the bend angle ω2 was 126 °.
[0059]
(Example 11)
A battery was manufactured in the same manner as in Example 1 except that a die die having a bending radius R0 of 0.65 mm was used for crimping, and the bending radius R1 of the outer case straight edge portion after crimping was 0.5 mm. Thus, a battery similar to that of Example 9 was obtained except that the bending radius R2 of the outer peripheral edge curve portion was 0.65 mm and the bending angle ω2 was 116 °.
[0060]
(Example 12)
A battery was manufactured in the same manner as in Example 1 except that a die mold having a bending radius R0 of 0.75 mm was used for crimping, and the bending radius R1 of the outer case peripheral straight portion after crimping was 0.7 mm. Thus, a battery similar to that of Example 9 was obtained except that the bending radius R2 of the outer peripheral edge curve portion was 0.75 mm and the bending angle ω2 was 115 °.
[0061]
(Example 13)
A battery was manufactured in the same manner as in Example 1 except that a die mold having a bending radius R0 of 0.9 mm was used for crimping, and the bending radius R1 of the outer case peripheral straight portion after crimping was 0.8 mm. A battery similar to that of Example 9 was obtained except that the bending radius R2 of the outer peripheral edge curve portion was 0.9 mm and the bending angle ω2 was 111 °.
[0062]
(Comparative Example 3)
A battery was manufactured in the same manner as in Example 9 except that a die mold having a bending angle ω0 of 90 ° was used for crimping, and the shape of the case tip after crimping was a curved line at the outer peripheral case peripheral straight part. Yes, the bending radius R1 is 0.6 mm at the outer R, the bending angle ω1 from the R start point to the end point (case tip) is 80 °, the shape of the peripheral curve portion is the bending radius R2 is 0.5 mm, and the bending angle ω2 is 80 A battery was obtained in the same manner as in Example 9 except for the temperature.
[0063]
Here, the bending radius R1 of the peripheral straight line portion is slightly larger than the bending radius R0 of the inner surface of the die mold, and this is considered to have returned after caulking by the spring back of the outer case.
[0064]
(Reference Example 5)
A battery was manufactured in the same manner as in Example 9 except that a die mold having a bending radius R0 of 0.35 mm was used for crimping, and the bending radius R1 of the outer case peripheral straight portion after crimping was 0.2 mm. Thus, a battery similar to that of Example 9 was obtained except that the bending radius R2 of the outer peripheral edge curve portion was 0.35 mm and the bending angle ω2 was 138 °.
[0065]
(Reference Example 6)
A battery was manufactured in the same manner as in Example 9 except that a die mold having a bending radius R0 of 1.05 mm was used for crimping, and the bending radius R1 of the outer case peripheral straight portion after crimping was 0.95 mm. Thus, a battery similar to that of Example 9 was obtained except that the bending radius R2 of the outer peripheral edge curve portion was 1.05 mm and the bending angle ω2 was 108 °.
[0066]
As described above, 100 batteries of Examples 9 to 13, Comparative Example 3, and Reference Examples 5 and 6 were manufactured. Measure the appearance defect rate of the battery, the incidence of open circuit voltage defective products and battery total high defective products after storage at 70 ° C-93% RH for 30 days, and the amount of curvature of the side wall of the interior case by sampling the 20 batteries after the test. The results are shown in Table 2.
[0067]
[Table 2]

[0068]
Even when the battery size and the plate thickness of the positive and negative electrode cases were different, substantially the same results as in the case of the 30 mm vertical and horizontal batteries described above were obtained.
In addition, the Example of this invention uses the flat nonaqueous solvent secondary battery which used the nonaqueous solvent for the nonaqueous electrolyte, and the flat square battery sealed by the crimping process at the time of making a positive electrode case into an exterior case However, it is also possible to replace the positive and negative electrodes and arrange a negative electrode case as an outer case. Furthermore, the present invention can be applied to other battery systems, and the same effect can be obtained with respect to the flat and square caulking seal.
[0069]
【The invention's effect】
As described above, according to the present invention, it is possible to prevent the deformation that occurs in the inner case and the spring back that occurs in the outer case peripheral straight portion at the time of caulking and sealing, and the sealing performance can be improved. A large flat battery can be provided.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a battery according to Example 1 of the present invention.
FIG. 2 is a plan view of the battery of Example 1 of the present invention.
FIG. 3 is an enlarged cross-sectional view of a sealing portion of a peripheral straight line portion of the battery of Example 1 of the present invention.
FIG. 4 is an enlarged cross-sectional view of a sealing portion of a peripheral curve portion of the battery of Example 1 of the present invention.
FIG. 5 is an enlarged cross-sectional view of a sealing portion of a peripheral straight line portion of a battery of a comparative example.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Exterior case (positive electrode case), 2 ... Positive electrode collector, 3 ... Flat spiral electrode group, 4 ... Interior case (negative electrode case), 5 ... Negative electrode collector, 6 ... Insulating gasket, 7 ... Die die, 8 ... Knockout pin, 9 ... Lower punch, 10 ... Conventional die die, A ... Peripheral curve portion, B ... Peripheral straight portion.

Claims

A metal outer case and a metal inner case are fitted to the flat surface of the battery through an insulating gasket in the vertical direction, and the outer case disposed on the outer peripheral side of the insulating gasket is further crimped. It has a sealed sealing structure, the thickness of the battery is smaller than the outer dimension, the peripheral portion has at least two peripheral linear portions, and each end of the linear portion is connected by a peripheral curved portion. In the flat rectangular battery, the caulking shape of the peripheral curved portion is a curve, and the outer case of the portion corresponding to the peripheral linear portion is intermediate between the front end of the outer case and the caulking bent portion. A flat rectangular battery characterized by being crimped into a shape provided with a straight portion.

The flat rectangular battery according to claim 1, wherein a bending radius of the crimped bending portion of the outer case is crimped to 1.5 to 4 times the outer case base plate thickness at the outer radius.

The flat rectangular battery according to claim 1, wherein a horizontal angle of a straight portion provided in the outer case with respect to a bottom surface of the outer case is crimped in a range of 25 ° to −15 °.